On an early June afternoon, the day after Eddy Merckx's sixtieth birthday, the greatest cyclist ever, rode for 40 miles near his home in the suburbs of Brussels with Lance Armstrong, the man who has inherited the 'cannibal's' status as the most redoubtable cyclist of his generation. 'He told me his plan for ending his career and made it clear to me that he did not contemplate being defeated in this Tour,' said Merckx. 'He said, "Another seven weeks and it's over." '

Like Merckx, Armstrong is not a man who has ever expected defeat and, as the American predicted to the old champion, he has come to the final day of his final Tour with his seventh victory in the bag.

As happened last year after Armstrong's sixth victory, the Texan will be compared with 'the cannibal', who dominated cycling between 1968 and 1977, winning 476 professional races in a 13-season career. Merckx won five Tours de France to Armstrong's probable seven, but he missed the race in 1973 to pursue other races and took a total of six wins in the other great Tours, Italy and Spain, neither of which Armstrong has won.

The 'cannibal' still has his distinguished air, his high cheekbones that some compared with those of a sphinx, and he is as combative as ever. Speaking to The Observer en route to this year's finale, Merckx was as keen to fight his corner as might have been expected of the most successful professional cyclist of all time. 'I was a more aggressive rider than Armstrong. I would attack more often. He waits for the other guys, then counter-attacks.'

Merckx acknowledged that Armstrong shares his insatiable hunger for victory 'particularly last year, when he won five stages', but added that the Texan 'races more in the style of [fellow five-times winners] Jacques Anquetil or Miguel Indurain'. 'Master Jacques' and 'Big Mig' were noted for targeting certain stages, whereas the Merckx way was to attempt to win every stage.

The 'cannibal' feels that the way he and Armstrong raced makes comparisons invidious. 'The two eras are totally different. I raced from 1 February to 31 October every year, competed for everything. When [like Armstrong] you are the best rider in the bunch and contest one race a year...." Merckx is too polite to say it, but the message is similar to that of another five-time winner, Bernard Hinault, who said: 'With Armstrong's racing programme, I would still be competing today and so would Eddy.'

There are similarities, however. Both have pushed the boundaries of dedication to their sport and both are perfectionists to the point of obsession. Merckx was legendary for getting up in the middle of the night to check his saddle height and had a cellar full of tyres; Armstrong has a workshop with a pile of discarded saddles that have failed to come up to scratch, he reconnoitres every mountain stage and receives constant updates on his rivals.

Merckx does not believe that the way Armstrong races is beneficial for the sport, with its sole emphasis on one race, the Tour de France, putting the rest of the calendar in the shade. 'It's not good for cycling, but how else can you race when the Tour is so important?' he said. 'The only event that counts is the Tour, it's the only race that all the media go to. It's far more important than it was in my time, but as I see it cycling is more than the Tour de France.'

The old champion and budding star first met when Armstrong raced on one of Merckx's bikes at the Barcelona Olympics in 1992. Subsequently, Merckx supplied bikes to the Texan's first professional team, Motorola, and the pair became close, particularly after Merckx's son, Axel - who will finish the Tour this year for the Davitamon-Lotto team - joined the squad.

'Eddy told me I could win a Tour de France some day, but that I needed to lose weight,' wrote Armstrong in his autobiography It's Not About the Bike .

The book has a photograph of Merckx, corpulent and suited, visiting a lean, frail-looking Armstrong in hospital when the Texan was in remission from testicular cancer in late 1996. Armstrong insisted that the 'cannibal' accompany him on his first bike ride after the illness.

'He was determined to come back to what he had been and I was impressed,' Merckx said recently in an interview with L'Equipe . 'No one believed in him at the time. Even I would never have thought he was capable of coming back and winning the Tour de France.'

The friendship between the two has become tense in public on one occasion only, when Merckx accused Armstrong of racing to make Axel lose in a big one-day event, the Liege- Bastogne-Liege, but the 'cannibal' feels that Armstrong has been misunderstood.

'The press has often been unjust where he is concerned,' he said. 'What is said about him has to be measured. Before his cancer he had already shown immense class, becoming world champion in Oslo in 1993, ahead of Indurain, who is not just a nobody.

'He didn't transform himself thanks to the grace of God, but by building on all his setbacks, by training like hell and sorting out his lifestyle. To begin with he ate anything, drank quite a few beers, even before a major race. The cancer slimmed him down, but it also weakened him, I believe, quite a bit, and that's why he has limited what he does to the Tour de France. Without the cancer he would have had a racing record far beyond the norm.'

As of this afternoon, when Armstrong rides up the Champs Elysees to win his seventh Tour, a new problem will confront him: dealing with retirement. Like many great athletes, Merckx had difficulty adapting to life outside sport - he famously said that at one point he could envisage no other existence than that of a professional cyclist - and he has some inkling of what awaits Armstrong.

'I stopped because I was tired of always racing,' said Merckx. 'It wasn't difficult for me to stop. I was mentally exhausted. But after that you need to find new goals, new things to aim for.' In Merckx's case, he put his energy into his bike factory, but it took him several years, in which his weight ballooned.

This week, even as he raced his last mountain stage, his last hill-top finish and watched his team defend the yellow jersey for the last time, Armstrong said that he has yet to feel any emotion about leaving racing behind; he was neither sad nor happy at the thought. Quite how the most competitively minded and obsessively dedicated cyclist since Merckx will cope remains to be seen.

His old mentor is optimistic, feeling that cancer has given Armstrong contact with the everyday world that many athletes lack.

'I don't know if Armstrong will find it hard to get into normal life. You can't really compare our cases,' said Merckx. 'He is a racer, too, but he has had cancer and has found other things in life which are important. He will find new goals to occupy his time without too much trouble.'